A pressure-sensitive adhesive usually has a storage elastic modulus [G'] at room temperature of about 1.times.10.sup.6 dyne/cm.sup.2 or lower as described in D. Satas, Adhesive Age, 31(9), 28(1988). When the storage elastic modulus of a pressure-sensitive adhesive at room temperature is increased, the pressure-sensitive adhesive becomes too hard and becomes non-adhesive. This is because a micro-contact of the pressure-sensitive adhesive and the adherend is not sufficiently carried out in the adhesive step as in a wrapping film for foods, namely, the wrapping films are visually (optically) adhered to each other, but the adhesion is not exhibited.
However, because a conventional pressure-sensitive adhesive has a softness in a sticky state having a tackiness, the pressure-sensitive adhesive adheres quickly. But, it is not easy to peel the pressure-sensitive adhesive adhered by lightly contacting, and thus, the correction of the position is difficult. Also, in processing such as cutting, punching, etc., of a pressure-sensitive adhesive sheet, there is a problem that the processing edge is stained with the pressure-sensitive adhesive.
If the storage elastic modulus of the pressure-sensitive adhesive is increased to solve these problems, the adhesive property is lowered along with the tackiness as described above, and thus the adhesion to an adherend is difficult without an adhesive assisting means such as heat treatment.
As described above, a pressure-sensitive adhesive which has a high elasticity and non-pressure-sensitive adhesion or low pressure-sensitive adhesion (tack free) capable of preventing lowering of adhesive workability, etc., and also is excellent in the adhesion has not yet been found.
Under such circumstances, an object of the present invention is to provide a pressure-sensitive adhesive composition which shows an excellent adhesion while exhibiting a high elasticity and tack free at about room temperature, and hence can cope with the adhesive workability and the adhesion, and a pressure-sensitive adhesive sheet having the composition.
Also, other object of the present invention is to provide the above-described pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets using the composition, which are excellent in the durability, the heat resistance, etc., and further to provide the above-described pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets using the composition, which are also excellent in the self-adhesion in addition to the durability such as the heat resistance, weather resistance, etc.
Other object of the present invention is to provide the above-described pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets using the composition, which show a good adhesion to various adherends and are excellent in the creep characteristics and the long-term durability and also is to provide the above-described pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets using the composition, which satisfy the creep resistance and the adhesion in a high temperature range and are excellent in the shock resistance in a low-temperature range.
Furthermore, still other object of the present invention is to provide the above-described pressure-sensitive adhesive sheets using a release liner not subjected to a silicone release coating and thus suitable for computer instruments which are liable to cause problems by the existence of a silicone, and in particular to provide the above-described pressure-sensitive adhesive sheets which are excellent in the releasing property of the above-described liner and show a good adhesive strength.
Also, other object of the present invention is to provide pressure-sensitive adhesive sheets which can be wound in a roll form without using a release liner and are suitable for the uses such as computer instruments as pressure-sensitive adhesive sheets containing substantially no silicone compound.